Filter screen

ABSTRACT

A filter strainer assembly for use in filtering apparatus having retaining lug means integral with a central portion thereof for holding the strainer assembly securely to a filter bed supporting plate. The strainer assembly includes a vertical center section, passing through the plate, having a passageway through a side portion thereof positioned above the plate and retaining lug means positioned below the plate. A resilient washer, which is in compression when the lug means is in its strainer securing position, is provided to compensate for material elongation. A passageway in the central section below the plate is formed by the lug means to permit gas accumulated under the plate to pass through the strainer.

llite States 1 atet 1 [111 3939,34

Weis et al. 1 May 1, 1973 [541 FILTER SCREEN FOREIGN PATENTS ORAPPLICATIONS Inventors: Frank Wells, Kansas City, 924,799 5/1963 GreatBritain ..210/293 Marvin E. Wood, Lenexa, Kans. 1,184,324 2/1959 France..210/293 [73] Assignee: Ecodyne Corporation, Chicago, Ill.

[22] Filed: Apr. 19, 1971 [21] Appl. No.: 135,263

[51] Int. Cl. ..BOld 29/08 [58] Field of Search ..210/274, 291, 292,210/293, 275, 289

[56] References Cited UNITED STATES PATENTS 3,468,422 9/l969 Camp..210/274 1,692,592 1 H1928 Stickney ..210/292 2,572,097 10/1951 Bakker..210/292 3,245,540 4/1966 Johnson 1 i ..210/291 3,498,462 3/1970Larrowe et al. ....2l0/293 X 1,111,471 9/1914 Krause ..210/292 3,472,38210/1969 Soriente et a1 ..210/293 X Primary ExaminerSamih N. ZaharnaAttorney-Charles M. Kaplan and Joel E. Siege] [57] ABSTRACT A filterstrainer assembly for use in filtering apparatus having retaining lugmeans integral with a central portion thereof for holding the strainerassembly securely to a filter bed-supporting plate. The strainerassembly includes a vertical center section, passing through the plate,having a passageway through a side portion thereof positioned above theplate and retaining lug means positioned below the plate. A resilientwasher, which is in compression when the lug means is in its strainersecuring position, is provided to compensate for material elongation. Apassageway in the central section below the plate is formed by the lugmeans to permit gas accumulated under the plate to pass through thestrainer.

6 Claims, 5 Drawing Figures riLrEn SCREEN BACKGROUND OF THE INVENTIONThis invention relates to underdrain strainers for filters, ion exchangebeds and the like.

A typical method of filtering a liquid is to pass the liquid through afilter bed of suitable filter media, such as sand or other granularmaterial well known in the art, which removes the suspended matter fromthe liquid. The filtered liquid passes through a plurality of underdrainstrainers secured to a bottom plate, which retains the filter bed, tothe underdrain compartment. The filtered liquid passes from theunderdrain compartment to the service line through suitable conduits.After a period of time the filter bed becomes clogged and fouled withsolid, foreign material, removed from the untreated liquid duringfiltration and, accordingly, becomes less efficient. As the filter bedbecomes clogged, the pressure differential between the upstream side andthe downstream side of the filter bed increases.

- One method of cleaning the filter bed is to backwash the bed withfiltered liquid. This step involves introducing a reverse flow offiltered liquid through the filter bed, via the strainers, to carry theforeign matter in the filter bed to waste. Some materials filtered fromthe raw liquid are sticky in nature and tend to adhere to the filtermedia and simple backwashing is not sufficiently effective to clean thebed after the filtering cycle. To overcome these deficiencies, a gascleaning or scouring cycle is utilized before the backwashing cycle. insuch a gas scouring cycle, air or other suitable gas under pressure isintroduced into the underdrain compartment of the filter chamber andpassed upwardly through the filter bed, via the strainers. As the airpasses through the filter bed, it violently agitates the filter mediaand thereby dislodges foreign material in the filter bed and foreignmaterial on the filter media. The backwash liquid then removes theforeign material from the filter chamber.

l-leretofore, underdrain strainers have utilized mounting bolts tofasten the strainers to the bottom plate, which have tended to WOl'k'lQOSe due to the fact that the strainers are under compression whilefiltering but the compression is relieved when backwashing the filtermedia. The tension in the mounting may also be relieved by temperatureelongation, creep and shipment vibration. Installation of such strainershave required the services of one man below the bottom plate and anotherman above the bottom plate. Further, prior art strainers do not providemeans to ensure that air is delivered to all the strainers during theair scour cycle.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a strainer for a filter and the like which issimple in construction and may be installed by one man without the useof special tools.

Another object is to provide a strainer for a filter and the like whichwill automatically maintain the correct mounting tension despiteelongation of parts due to temperature or creep.

A further object is to provide a strainer for a filter and the likewhich eliminates the use of mounting bolts which have a tendency to workloose during the continual cycling changes and due to shipmentvibration.

A still further object is to provide a strainer for a filter apparatusof the type providing a gas scouring cycle which ensures gas delivery toall strainers during the gas scouring cycle.

Another object is to provide a strainer for a filter and the like whichwill, during the backwash of the filter bed, afford cleaning of the areaimmediately between the strainers.

Briefly, the invention comprises a strainer composed of two parts, ahollow frustro-conical strainer member having a plurality of aperturesor ports in its conical sidewall, and a vertical tubular center sectionpassing through a central aperture in the top of the strainer member.The center section includes a head portion closing off the top portionthereof and positioned immediately above the central strainer aperture.A resilient washer is positioned between the head portion and the top ofthe strainer member. A plurality of retaining lugs, integral with thecenter section, are provided to contact the bottom surface of the platesupporting the filter media and thereby tension the strainer memberbetween the head portion and the plate. A passageway is provided in thecentral section below the filter media supporting plate to permit gasfrom below the plate to pass therethrough and then upward through thecenter section into the strainer member through a passageway in thecentral section above the plate. The apertures in the strainer sidewallextend only through approximately the lower half thereof so as to createa swirling effect in the filter media during the backwash cycle.

The invention, both as to its organization and method of operation,taken with further objects and advantages thereof, will be understood byreference to the following description taken in conjunction with theaccompanying drawings, in which:

DESCRlPTlON OF THE DRAWINGS F116. 1 is a side elevational view,partially in section, illustrating a filter having a strainers embodyingthe feaures of the present invention;

FIG. 2 is a vertical sectional view illustrating an underdrain strainerembodying features of the present invention;

ElG. 3 is a side elevational view of the strainer center section;

EKG. is a bottom view of the strainer member; and

FIG. 5 is an enlarged vertical sectional view of a portion of thestrainer member illustrating the slots passing through the sidewall.

DESCRlPTlON OF A PREFERRED EMBODIMENT Referring now to the drawings, andmore particularly to FIG. l, there is illustrated a simplified exemplaryfilter Ml utilizing the strainers of the present invention. Filter has afilter bed 12 through which the raw liquid is passed during the servicecycle to remove solid foreign materials therefrom. Filtered water fromfilter 10 is passed to service. After filter bed 12 has become cloggedwith foreign particles removed from the raw liquid, a gas scouring cycleis initiated wherein pressurized gas is passed upwardly threrthrough todislodge foreign matter in bed 12. After filter bed 12 has been gasscoured, it is backwashed with treated liquid to remove the foreignmaterial therefrom.

More specifically, filter comprises a cylindrical tank 11 having a falsebottom plate 13 dividing tank 11 into an inlet chamber 14 and anunderdrain outlet chamber 15. Filter bed 12 of suitable filter media,such as sand or the like, is situated in filter chamber 14 on bottomplate 13. An inlet pipe 16 extends into and communicates with inletchamber 14 to carry raw liquid into chamber 14. Outlet pipe 17communicates with underdrain chamber to pass the treated water fromchamber 15; to service. A gas scour inlet pipe 18, has one end in fluidcommunication with outlet pipe 17 and the other end in fluidcommunication with a source of pressurized gas (not shown). Backwashinlet pipe 19 has one end in fluid communication with outlet pipe 17 andthe other end in fluid communication with a backwash storage tank (notshown). A transfer pipe 20 communicates with inlet pipe 16 to carrybackwash water from chamber 14. Conventional control valves 21, 22, 23,24, and are associated respectively with pipes 16, 17, 18, 19, and 20 tocontrol fluid flow therethrough.

Underdrain strainers 30, embodying the features of the presentinvention, are secured to bottom plate 13. Referring to FIGS. 2-5,strainer includes a strainer member 40, a center section 50 andfastening means 60. As best seen in FIG. 2, strainer member comprises ahollow member of generally frusto-conical shape formed by a plurality ofvertical ribs 41 extending between an upper support ring 42 and a lowersupport ring 43. A plurality of closely spaced arcuate horizontal ribs44, having a wedge-shaped vertical cross section, are formed betweenadjacent vertical ribs 41 to form a plurality of small apertures orslots 45, which prevent the filter media or the like from passingthrough strainer member 40 to underdrain chamber 15 during the servicecycle. Ribs 44 only extend between the lower halves of ribs 41, abovewhich are formed filler members 46 which prevent the flow of fluidthrough the upper portion of strainer member 40. Member 40 has anopening 47 through ring 42 and an opening 48 through ring 43. Strainermember 40 is preferrably injection molded of a plastic material, i.e.,nylon.

Center section 50, as seen in FIGS. 2 and 3, includes a tubular member51, which passes through an opening 59 in bottom plate 13, having anupper section 52 positioned within member 40 above plate 13 and a lowersection 53 positioned within chamber 15 below plate 13. Upper section 52extends through aperture 47 in member 40 and has a head portion 54closing off the top portion thereof. A tension compensating washer 55 issandwiched between head portion 54 and ring 42. Apertures 56 in section52 permit fluid communication between the interior of member 40 and theinterior of section 52. Section 53 has an open bottom end 57.

Fastening means 60, as seen in FIGS. 2 and 3, includes a pair ofretaining lugs 62, formed integral with an upper portion of section 53to contact the lower surface of plate 13 and wedge member 40 between theupper surface of plate 13 and washer 55 and head portion 54. Lugs 62have bottom portions 63 integral with section 53, and side portions andupper portions 64 and 65 respectively spaced a short distance from thesurface of section 53, so as to permit a small amount of inward movementof lugs 62 and thus allow them to be forced through openings 47 and 59.As seen in FIG. 3 the spacing between side portion 64 and the surface ofsection 63 results in a pair of gas metering slots 66. Side portions Mare inclined upwardly and outwardly such that as center section 50 isforced downward through openings 47 and 59, lugs 62 are forced inward asthey pass through the openings and snap outward after they have passedtherethrough into a locking position. The diametrical distance betweenthe upper portions of lugs 62 is greater than the diameter of opening59. Upper portions 65 include top surfaces 67 which are slightlyinclined downwardly and outwardly to fascilitate engagement with thebottom surface of plate 13. Lugs 62 are vertically positioned on section53 such that when top surfaces 67 lock in contact with the bottomsurface of plate 13, washer 55 is compressed between head 54 and member40.

Bottom plate 13 has a plurality of openings 59 symmet ically spacedtherethrough, each of which has a strainer 30 associated therewith.Strainers 30, embodying features of the present invention, may beinstalled by one man in a simple three step operation. First, washer 55is positioned about upper section 52 adjacent head portion 54by forcingit upward past lugs 62. Second, center section 50 is attached tostrainer member 40 by passing section 50 downward through opening 47. Asside portions 64 of lugs 62 contact the periphery of opening 47 theupper portions 65 of lugs 62 move inward permitting lug 62 to passentirely therethrough. After lugs 62 have passed through opening 47, andtherefore side portions 64 are no longer in contact with the peripheryof opening 47 lugs 62 snap back to their original position whichprevents the separation of section 50 from strainer member 40. Third,the lower section 53 is passed through opening 59 to attach strainer 30in place on bottom plate 13. As side portions 64 of lugs 62 contact theperiphery of opening 59 the upper portions 65 of lugs 62 move inwardlypermitting lug 62 to pass entirely therethrough. As the top surfaces 67of upper portions 65 clear the bottom of plate 13, lugs 62 snap backinto their original or locked position wherein the surfaces 67 contactthe bottom of plate 13. Surfaces 67 are vertically positioned on section53 such that in order for surfaces 64 to clear the bottom of plate 13 asmall compressing force must be applied to washer 55 by sandwichingwasher 55 between head portion 54 and ring 42. Thus, strainer member 30is securely fastened to plate 13 and since washer 55 is in compression asmall degree of material elongation may be compensated for withouteffecting the securement of strainer 30 to plate 13. Further, vibrationresulting from shipment of filter 10 will likewise not effect theattachment of strainer 30.

in operation of filter 10, during the filtering or service cycle valves21 and 22 are open and valves 23, 24, and 25 are closed. Raw liquidpasses through inlet pipe 16 into inlet chamber 14 and then passesthrough filter bed 12. The filtered liquid then passes through strainers30 to underdrain chamber 15 and out through outlet pipe 17 to service.The filtered liquid passes through slots 45 into member 40 and thenthrough apertures 56 into center section 50 before entering underdrainchamber 15. After filter bed 12 has become clogged with foreignparticles removed from the raw liquid, a gas scouring cycle isinitiated. During the gas scouring cycle valves 23 and 25 are open andvalves 21, 22 and 24!- are closed. pressurized gas (i.e., air) isbubbled through pipes 18 and 17 into underdrain chamber 15. As the airin chamber rises, a portion of it enters bottom opening 57 in section53, and the remainder continues to rise and passes through meteringslots 65 into section 53. The air then passes through apertures 56 intomember 40 and out through slots 45 into inlet chamber 14. As the airpasses up through filter bed 12, the air agitates bed 12 and causes theforeign particles which have collected therein to become disengaged fromthe filter media. The scouring air passes out of inlet chamber 14through transfer pipe 20. Metering slots 62 insure an even distributionof air through all the strainers 3t) and prevent the accumulation of airin the upper portion of underdrain chamber 15. Upon completion of thegas scouring cycle the backwash cycle begins. During the backwash cyclevalves 2 and are open and valves 21, 22 and 23 are closed. Filteredliquid from a storage chamber (not shown) pass through pipes 19 and 17into underdrain chamber 15, up through center section 50 into member 40,out slots 45 and through filter bed 12, and then out through transferpipe 20 to drain. This flow of backwash liquid through filter bed 12removes the foreign material which accumulated therein during theservice cycle.

The filtering apparatus 10, as disclosed above is for exemplary purposesand should not be construed to indicate that the strainers disclosedtherewith do not have utility in conjunction with other types offiltering apparatus. While the embodiments discribed herein are atpresent considered to be preferred, it will be understood that variousmodifications and improvements may be made therein and it is intended tocover in the appended claims all such modifications and improve ments asfall within the true spirit and scope of the invention.

What is claimed:

1. In an apparatus including a filter bed and a bottom plate supportingsaid bed, said bottom plate having at least one opening; the improvementbeing a strainer assembly comprising:

a. a hollow conically shaped strainer member resting on said bottomplate, said strainer member having a plurality of apertures passingthrough the sidewall thereof, said strainer member having a centralopening through an upper surface thereof in alignment with the openingin said bottom plate;

b. a substantially vertical tubular center section passing through saidbottom plate opening and said strainer member central opening, saidcenter section having a head portion closing off the upper portionthereof of greater diameter than the diameter of said strainer membercentral opening, said center section further having a passageway througha side portion thereof positioned above said bottom plate to permitfluid communication between the interior of said strainer member and theinterior of said central section; and

. retaining lug means integral with said central section to hold saidstrainer assembly in position on said bottom plate, said retaining lugmeans including at least two lug sections cut from a portion of saidcentral section immediately below said bottom plate having a bottomportion integral with said central section and side and upper portionsspaced a short distance from said central section so as to permit asmall amount of inward movement of said upper portion of said lugsection to allow said lug section to pass through said bottom plateopening and to permit gas accumulated in the upper portion of saidfilter tank outlet side to pass therethrough into said central section.

2. The invention of claim 1 wherein a resiliant washer means istensioned between said center section head portion and the upper surfaceof said strainer means.

3. The invention as defined in claim 1 wherein said upper portion havingan outside diameter greater then the diameter of said bottom plateopening and a horizontal upper surface associated therewith for contactwith the lower surface of said bottom plate.

4. In a filter apparatus of the type providing a serivce cycle, a gasscouring cycle, a backwash cycle, and including a filter tank, abackwash supply means, and means for providing a gas under pressure,said filter tank having an upper inlet side and a lower outlet side witha filter bed supported upon a bottom plate therebetween; the improvementbeing a strainer assembly comprising:

a. a strainer member attached to the upper surface of said bottom plate,said strainer member having a plurality of apertures passing through thesidewalls thereof;

b. a substantially vertical tubular member passing through an aperturein said bottom plate having an upper section positioned within saidstrainer means and a lower section extending into said filter tankoutlet side, said upper section having apertures therethrough such thatthe interior of said upper section is in fluid communication with theinterior of said strainer means, said lower section having an openbottom end and a passageway passing through a portion of said lowersection positioned immediately below said bottom plate so as to permitgas accumulated in the upper portion of said filter tank outlet side topass therethrough into said lower section of said tubular member;

. said backwash supply means and said means for providing gas underpressure being in communication with said filter tank outlet side;

d. said strainer member includes an upper surface having an aperturetherethrough;

e. said upper section of said tubular member having a portion passingthrough said aperture in said upper surface of said strainer member;

f. said upper section of said tubular member having a head portionclosing off the top thereof of greater diameter than the diameter ofsaid aperture in said upper surface of said strainer member;

g. retaining lug means integral with the lower section of said tubularmember to contact the lower surface of said bottom plate and therebyhold said strainer member in position on said bottom plate;

h. said retaining lug means includes at least two lug sections cut fromsaid lower section of said tubular member, said lug sections having anupper portion with an outside diameter greater than the diameter of saidaperture in said bottom plate;

i. said lug sections having a bottom portion integral with said lowersection of said tubular member and side and top portions spaced a shortdistance from said lower section of said tubular member so as to permita small amount of inward movement of said washer means is tensionedbetween said upper surface of said strainer member and said headportion.

6. The invention of claim 4- wherein said strainer member means isinjection molded of a plastic materitop portion of said lug section, andthus allow said lug section to pass through said aperture in said bottomplate; and

j. said passageway passing through said lower section permitting gasaccumulated in the upper portion of 10 said filter tank outlet side topass therethrough into

1. In an apparatus including a filter bed and a bottom plate supportingsaid bed, said bottom plate having at least one opening; the improvementbeing a strainer assembly comprising: a. a hollow conically shapedstrainer member resting on said bottom plate, said strainer memberhaving a plurality of apertures passing through the sidewall thereof,said strainer member having a central opening through an upper surfacethereof in alignment with the opening in said bottom plate; b. asubstantially vertical tubular center section passing through saidbottom plate opening and said strainer member central opening, saidcenter section having a head portion closing off the upper portionthereof of greater diameter than the diameter of said strainer membercentral opening, said center section further having a passageway througha side portion thereof positioned above said bottom plate to permitfluid communication between the interior of said strainer member and theinterior of said central section; and c. retaining lug means integralwith said central section to hold said strainer assembly in position onsaid bottom plate, said retaining lug means including at least two lugsections cut from a portion of said central section immediately belowsaid bottom plate having a bottom portion integral with said centralsection and side and upper portions spaced a short distance from saidcentral section so as to permit a small amount of inward movement ofsaid upper portion of said lug section to allow said lug section to passthrough said bottom plate opening and to permit gas accumulated in theupper portion of said filter tank outlet side to pass therethrough intosaid central section.
 2. The invention of claim 1 wherein a resiliantwasher means is tensioned between said center section head portion andthe upper surface of said strainer means.
 3. The invention as defined inclaim 1 wherein said upper portion having an outside diameter greaterthen the diameter of said bottom plate opening and a horizontal uppersurface associated therewith for contact with the lower surface of saidbottom plate.
 4. In a filter apparatus of the type providing a serivcecycle, a gas scouring cycle, a backwash cycle, and including a filtertank, a backwash supply means, and means for providing a gas underpressure, said filter tank having an upper inlet side and a lower outletside with a filter bed supported upon a bottom plate therebetween; theimprovement being a strainer assembly comprising: a. a strainer memberattached to the upper surface of said bottom plate, said strainer memberhaving a plurality of apertures passing through the sidewalls thereof;b. a substantially vertical tubular member passing through an aperturein said bottom plate having an upper section positioned within saidstrainer means and a lower section extending into said filter tankoutlet side, said upper section having apertures therethrough such thatthe interior of said upper section is in fluid communication with theinterior of said strainer means, said lower section having an openbottom end and a passageway passing through a portion of said lowersection positioned immediately below said bottom plate so as to permitgas accumulated in the upper portion of said filter tank outlet side topass therethrough into said lower section of said tubular member; c.said backwash supply means and said means for providing gas underpressure being in communication with said filter tank outlet side; d.said strainer member includes an upper surface having an aperturetherethrough; e. said upper section of said tubular member having aportion passing through said aperture in said upper surface of saidstrainer member; f. said upper section of said tubular member having ahead portion closing off the top thereof of greater diameter than thediameter of said aperture in said upper surface of said strainer member;g. retaining lug means integral with the lower section of said tubularmember to contact the lower surface of said bottom plate and therebyhold said strainer member in position on said bottom plate; h. saidretaining lug means includes at least two lug sections cut from saidlower section of said tubular member, said lug sections having an upperportion with an outside diameter greater than the diameter of saidaperture in said bottom plate; i. said lug sections having a bottomportion integral with said lower section of said tubular member and sideand top portions spaced a short distance from said lower section of saidtubular member so as to permit a small amount of inward movement of saidtop portion of said lug section, and thus allow said lug section to passthrough said aperture in said bottom plate; and j. said passagewaypassing through said lower section permitting gas accumulated in theupper portion of said filter tank outlet side to pass therethrough intosaid lower section of said tubular member being formed by the spacingbetween said lower section of said tubular member and said side and topportions of said lug section.
 5. The invention of claim 4 wherein aresiliant washer means is tensioned between said upper surface of saidstrainer member and said head portion.
 6. The invention of claim 4wherein said strainer member means is injection molded of a plasticmaterial.